1. Field of the Invention
The present invention relates to an antenna control method of and an antenna controller for controlling the direction of an antenna beam of an antenna used for either a satellite communication earth station installed in a mobile body, such as an aircraft, or a satellite broadcast receiving facility.
2. Description of the Prior Art
FIG. 10 is a block diagram showing the structure of a prior art antenna controller used for a satellite broadcast receiver for use in aircraft, as disclosed in Japanese patent application publication (TOKKAIHEI) No. 50102895, for example. In the figure, reference numerals 11-1 to 11-n denote receive blocks each of which receives an electric wave from a geostationary satellite by way of its antenna, respectively, reference numeral 12 denotes a common-mode synthesizer for synthesizing n outputs of the antennas of the plurality of receives blocks 11-1 to 11-n after making them in phase with each other, reference numeral 13 denotes on inertial navigation system installed in a mobile body such as an aircraft, reference numeral 15 denotes an orbit data processor for converting orbit data 14 on a geostationary satellite into an electric signal, reference numeral 16 denotes a tracking control unit for generating an electric signal used for mechanical tracking control of the plurality of receive blocks 11-1 to 11-n based on a signal from the inertial navigation system 13 and the signal from the orbit data processor 15, and for sending the generated electric signal to a driving mechanism 17 mechanically connected to the plurality of receive blocks 11-1 to 11-n, and reference numeral 18 denotes a receiver for receiving a satellite broadcast based on an output of the common-mode synthesizer 12.
Each of the plurality of receives blocks 11-1 to 11-n shown in FIG. 10 includes a flat antenna and a BS converter. Each receive block receives an electric wave from the satellite by way of its antenna and then converts the electric wave received to a first intermediate-frequency signal with its BS converter. The common-mode synthesizer 12 converts each of a plurality of first intermediate-frequency signals from the plurality of receives blocks 11-1 to 11-n to a second intermediate-frequency signal, and then synthesizes a plurality of a second intermediate-frequency signals to generate a composite signal after making them in phase with each other and outputs the composite signal to the receiver 18.
On the other hand, the tracking control unit 16 generates a signal used to control the mechanical tracking of the antenna of each of the plurality of receive blocks 11-1 to 11-n based on an electrical signal from the inertial navigation system 13 installed in the mobile body, which indicates navigation information (i.e., motion information on a motion of the mobile body), and the electrical signal generated by the orbit data processor 15 based on the orbit data 14 on the broadcasting satellite which was input from the outside of the antenna controller in advance, and the tracking control unit 16 then sends the generated signal to the driving mechanism 17. The driving mechanism 17 directs the antenna of each of the plurality of receive blocks 11-1 to 11-n toward the broadcasting satellite according to the signal used for mechanical tracking control from the tracking control unit 16. The prior rat antenna controller can thus excellently receive electric waves from the broadcasting satellite whether the mobile body, such as an aircraft, including the controller has an arbitrary attitude, by controlling the mechanical tracking of the antenna of each of the plurality of receive blocks 11-1 to 11-n.
By the way, it is necessary to mount active devices included in the antenna controller in a place of the mobile body where the best possible operating condition is ensured, for instance, a pressure cabin in the case of an aircraft, from the viewpoint of reliability. The prior art antenna controller as shown in FIG. 10 thus omits a circuit for detecting the direction in which electric waves are coming, which is part of an active device, by using motion information output from the existing inertial navigation system 13, thus simplifying the antenna controller and improving the reliability of the apparatus.
A problem with the prior art antenna controller constructed as above is that although it is possible to direct the antenna beam toward the broadcasting satellite when the beamwidth of the antenna of each of the plurality of receive blocks is relatively large, it is impossible to direct the antenna beam toward the broadcasting satellite with a high degree of accuracy when the beamwidth of the antenna of each receive block is small because a delay of motion information output from the inertial navigation system negatively affects the tracking accuracy.
In general, information output from the inertial navigation system has an uncertain delay. Assuming that motion information on the true bearing from the inertial navigation system has a delay of 100 msec when the mobile body is an aircraft, if the mobile body inclines rapidly in 30 degrees/s with respect to the true bearing, an error of 3 degrees or less occurs in the inclination of the aircraft though it depends on the direction of the broadcasting satellite and the update cycle of the inertial navigation system. Then, the prior art antenna controller will be unable to catch the direction of the broadcasting satellite momentarily if the beamwidth of the antenna is about 2 degrees. Even if the prior art antenna controller is equipped with a monopulse tracker, the delay of information output from the inertial navigation system is fatal to the system if it has a small antenna beam width because it is thought that the system cannot deal with rapid occurrence of such errors.
The present invention is proposed to solve the above-mentioned problem, and it is therefore an object of the present invention to provide an antenna control method of and an antenna controller for estimating a delay of navigation information, i.e., motion information sent from an inertial navigation system, estimating current or future motion information on a mobile body such as an aircraft in consideration of the estimated delay, so as to direct an antenna beam toward a geostationary satellite or a mobile satellite with a high degree of accuracy.
In accordance with an aspect of the present invention there is provided an antenna control method for controlling a direction of an antenna beam of an antenna unit installed in a mobile body, for a purpose of satellite communication or satellite broadcast reception using a satellite, the method comprising the steps of: in order to estimate a delay of motion information on a motion of the mobile body which is acquired by an inertial navigation system, separately acquiring motion information on the motion of the mobile body; estimating the delay of the motion information acquired by the inertial navigation system based on the motion information separately acquired in the previous step and the motion information acquired by the inertial navigation system; and calculating a direction of the antenna beam in consideration of the estimated delay to direct the antenna beam toward the satellite.
In accordance with another aspect of the present invention, the separately acquiring step is the step of acquiring the motion information on the motion of the mobile body by using a 3-axis angular-velocity sensor.
In accordance with a further aspect of the present invention, the separately acquiring step is the step of acquiring the motion information on the motion of the mobile body by using a 3-axis magnetic bearing sensor.
In accordance with another aspect of the present invention, there is provided an antenna controller for controlling a direction of an antenna beam of an antenna unit, which is installed in a mobile body, for receiving an electric wave from a geostationary satellite, for a purpose of satellite communication or satellite broadcast reception using the geostationary satellite, the antenna controller comprising: an antenna beam control unit for controlling the direction of the antenna beam of the antenna unit; an inertial navigation system for acquiring motion information on a motion of the mobile body; an antenna beam direction calculation unit for calculating the direction of the antenna beam based on the motion information from the inertial navigation system to direct the antenna beam toward the geostationary satellite; a motion information acquisition unit for separately acquiring motion information on the motion of the mobile body; and a motion estimation unit for estimating a delay of the motion information acquired by the inertial navigation system based on the motion information acquired by the inertial navigation system and the motion information acquired by the motion information acquisition unit, and for estimating motion information to be sent to the antenna beam direction calculation unit in consideration of the estimated delay.
In accordance with a further aspect of the present invention, the motion information acquisition unit has a 3-axis angular-velocity sensor.
In accordance with a further aspect of the present invention, there is provided an antenna controller for controlling a direction of an antenna beam of an antenna unit, which is installed in a mobile body, for receiving an electric wave from a mobile satellite, for a purpose of satellite communication or satellite broadcast reception using the mobile satellite, the antenna controller comprising: an antenna beam control unit for controlling the direction of the antenna beam of the antenna unit; an inertial navigation system for acquiring motion information on a motion of the mobile body; an antenna beam direction calculation unit for calculating the direction of the antenna beam based on the motion information from the inertial navigation system to direct the antenna beam toward the mobile satellite; a satellite position information generation unit for generating position information on the mobile satellite from one minute to the next and for sending the position information to the antenna beam direction calculation unit; a motion information acquisition unit for separately acquiring motion information on the motion of the mobile body; and a motion estimation unit for estimating a delay of the motion information acquired by the inertial navigation system based on the motion information acquired by the inertial navigation system and the motion information acquired by the motion information acquisition unit, and for estimating motion information to be sent to the antenna beam direction calculation unit in consideration of the estimated delay.
In accordance with another aspect of the present invention, the motion information acquisition unit has a 3-axis angular-velocity sensor.
In accordance with a further aspect of the present invention, the motion information acquisition unit has a 3-axis magnetic bearing sensor.
Accordingly, the antenna controller according to the present invention can direct the antenna beam of the antenna unit toward either a geostationary satellite or a mobile satellite with a high degree of accuracy.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.